1. Field of Invention
This invention relates to automatic test systems for digital electronic converters and particularly to statistical methods and related electronic apparatus for testing analog-to-digital converters.
Converters between the digital and analog signal domains are employed to interface digital electronic circuitry and analog devices. Accuracy of conversion, gain and repeatability in the process of conversion are matters of concern. One method of testing an analog-to-digial converter is to apply a digital signal to the input of a digital-to-analog converter to obtain an analog output signal, and then to apply the analog output signal to the input of the analog-to-digital converter under test to recover a digital signal and then to compare the digital output signal with a standard such as the digital input signal or to process the output signal to determine its statistical characteristics. The characteristics of the output signal in terms of a statistical description provide an indication of the accuracy of the analog-to-digital converter.
2. Description of the Prior Art
State of the art testing techniques for digital converters are generally limited to testing a few states such as the simple binary weights and full-scale amplitude. Substantially all tests are static in nature and are incapable of providing a complete statistical evaluation of a converter.
One of the concerns of prior art converter testing methods has been an inability to distinguish between signal-induced biases or errors and biases or errors inherent in the testing devices. Accordingly, much effort has been devoted to linearization of the excitation signals and of the transfer characteristics of the measuring devices, such as the digital-to-analog converter used as a voltage reference to provide a calibrated input to the analog-to-digital converter under test. The present invention represents a departure from this effort to idealize the testing equipment.
3. Cross-Reference to Related Applications
In the copending patent application entitled "Method and Apparatus for Digital Converter Testing," Ser. No. 204,979, filed Nov. 7, 1980, a method and apparatus are disclosed for dynamically testing the overall performance characteristics of both digital-to-analog converters and analog-to-digital converters. The method comprises dynamically exercising an analog-to-digital or digital-to-analog converter with, respectively, analog or digital signal patterns which can be characterized as the sum of a set of mutually orthogonal two-state functions of defined amplitudes, the sum having substantially uniform amplitude distribution over the allowable states of the amplitude range in order to exercise substantially all allowable converter states of concern. Thereafter, the response of the converter under test is examined for a number of basic performance parameters, including total distortion, linearity and optimum gain. The method described therein yields a relatively complete statistical description of the performance characteristics. The disclosures of that application and the other copending patent application entitled "Method for Analyzing a Digital to Analog Converter with a Nonideal Analog to Digital Converter", Ser. No. 264,928, filed May 18, 1981, are incorporated herein by reference and made a part hereof.